Administration of sterile solutions is required for many prescription and non-prescription materials. In general, such solutions, and the dispensers in which they are stored, are sterilized prior to closure of the dispenser. Contamination can occur, however, after the dispenser is opened and used. Various approaches have been employed in attempts to decrease this contamination problem.
Single dose dispensers are available. Such dispensers, however, are made only for one time use, and are then discarded, adding considerably to packaging costs. Moreover, more sterile solution than is required for a single dose is usually packaged which also adds to the expense of the treatment. Another problem is that persons may attempt to use the single dose dispenser multiple times, which can result in contaminated liquid being dispensed.
Alternatively, preservatives have been added to multi-dose dispensers to prevent microbial contamination after the dispenser is initially used. Such preservatives, however, are often toxic to mammalian cells, as well as microbial cells. For example, many preservatives used in eye drop formulations are toxic to the goblet cells in the eye. Such toxicity is detrimental to persons requiring prolonged application of the solutions. Moreover, persons often develop chemical sensitivity to the preservative, resulting in significant allergic reactions to the preparations. Such allergies can appear in some persons after prolonged exposure, as well as in others after only a single exposure.
Membrane filters have also been used in liquid dispensers in attempts to prevent microbial contamination of the stored sterile liquid. If a hydrophilic filter is used, however, the filter can allow the phenomenon known as "grow-through," in which microbial progeny on the downstream (non-sterile) side of the filter can pass through the filter pores because of their smaller size during cell division, and thereby contaminate the sterile solution contents in the dispenser.
Hydrophobic filters have also been employed in liquid dispensers. Hydrophobic surfaces are non-wetting, and therefore are significantly more difficult for microbes to grow on. Such filters, however, because of their hydrophobicity will not allow the flow of sterile aqueous solutions through the filter.